New Contact Property Option or Calculation Option
What we want is a metric that shows how many pages a contact has viewed before they submitted their first form. To do this we'd need one piece of data not currently supplied in HubSpot: date of each pageview. With that, we could compare each pageview date to the first form submission date and aggregate the results to show how many pages were viewed before a contact submitted the form.
So either HubSpot could create that property (loop through pageview dates, compare to first conversion date, add to total if true, return total) or add the ability to loop through another property like pageviews and compare dates.